Custom link type that attaches file in :follow

[Tarjei Bærland]

Hi!

I am having some trouble adding a link via =org-link-set-parameters=.

I want to have a custom =xournalpp=-link type that behaves as follows:
- follow :: Open attached file
  - exists :: open the file
  - don't exist :: create attachment directory and copy template file into it
- export :: Use [[https://xournalpp.github.io/][Xournalpp]] to export the file 
as an svg. Inline this svg.

#+begin_src emacs-lisp
  (org-link-set-parameters
   "xournalpp"
   :follow (lambda (path)
             (let ((xoppfile (concat (org-attach-dir-get-create) "/" path))
                   (template "/home/tarjei/repos/konturer/maler/skisse.xopp"))
               (cond ((not (file-exists-p xoppfile)) (copy-file template 
xoppfile)))
               (org-attach-sync)
               (shell-command (format "xournalpp %s" xoppfile))))
   :export (lambda (path desc backend)
             (let ((xoppfile (concat (org-attach-dir-get-create) "/" path))
                   (tempfile "/home/tarjei/temp/xournal_export.svg"))
               (shell-command (format "xournalpp --create-img %s %s" tempfile 
xoppfile))
               (with-temp-buffer
                 (insert-file tempfile)
                 (buffer-string)))))

#+end_src

Something seems to go wrong during the export, however, where a new attachment 
directory is created. Is my assumption that the export will run with =point= at 
the link incorrect?

All other feedback on the implementation would be much appreciated, I seem to 
repeat myself way more than should be necessary.

Regards,
Tarjei Bærland